This invention relates in general to a mounting for a rotating shaft and, more particularly to a mounting that retains stiffness through temperature variations.
A rotating shaft requires support of one type or another, and typically that support derives from a housing in which the shaft or at least a portion of it rotates, usually on some type of antifriction bearing. This type of bearing has an inner race around the shaft, an outer race in the housing and rolling elements between the two races to enable the inner race to rotate with minimal friction within the outer race and, of course, the shaft within the housing. The shaft normally transfers torque, and steel is best suited for this purpose. The components of the bearing must resist cyclic loads of substantial magnitude, and again, steel is the most practical material, particularly steel which has been case hardened or through hardened. But, being around the bearing and shaft, the housing has a larger cross-section to transfer loads. To reduce weight, the housing is often formed of a light weight metal, aluminum being typical. The coefficients of thermal expansion for light weight metals, such as aluminum, exceed the coefficients for various steels, and this produces differential thermal expansion which detracts from the stability of the shaft.
For example, the typical drive axle for a rear wheel drive vehicle has a housing containing a ring gear and a pinion gear which meshes with the ring gear. The pinion gear should rotate with stability to assure minimal fatigue and wear. To this end, the shaft on which it is mounted may be confined by a double row tapered roller bearing set to a condition of slight preload, thus eliminating radial and axial play within the bearing. A slight interference fit between the inner race or cones of the bearing and the shaft eliminates radial motion between the shaft and inner race. The outer race usually fits into the housing with a tight fit and typically takes the form of a double cup having a flange at one end. The flange fits against the exterior face of the housing to which it is secured with machine screws that thread into the housing. Even though a tight fit may exist between the double cup and the housing at assembly, that fit may disappear during operation owing to differential thermal expansion. When that occurs, only the flange supports the bearing in the housing, and the screws which secure it often do not prevent the bearing and the shaft from displacing radially in the housing.